Conventional digital copying machines include, for example, those machines wherein a storage medium with a large capacity is installed and inputted image data is accumulated in the storage medium, while the image data is read out on demands from the storage medium so as to be released as visible images. In such apparatuses, it is necessary to effectively utilize the limited storage capacity and also to effectively accumulate necessary image data within the storage capacity. For this reason, as for image data already stored in the storage medium, the user of the conventional copying machine has to conduct data compression with respect to image data that is relatively less important, or erase such data, in response to input of new image data or other operations.
For example, the following technique has been proposed as a technique for data compression in the apparatus having the storage function for image data. Japanese Laid-Open Patent Publication No. 277980/1992 (Tokukaihei 4-277980) discloses an apparatus for reading and storing image data, which is capable of minimizing the amount of data to be stored by a modified arrangement wherein, upon receipt of a lengthwise image, the image is rotated by 90 degrees to form data of an oblong image, and then the data is subjected to compression.
This arrangement is described below in detail. Unlike character data, data (image data, which is binary coded data representative of image information requires a tremendous storage capacity for its storage. In order to reduce the necessary storage capacity, the image data is stored in a compressed manner. Utilizing the fact that image data consists of continuous white or black information, the compression is carried out by counting how many pieces (how many dots) of white or black information continue. Upon reading image information, the image information is binary coded and read by scanning the image in the lateral direction and further shifting the scanning position successively in the longitudinal direction within a reading area. The scanning in the longitudinal direction is set to reach the lower end of a document. In this arrangement, even in the case of documents of the same size, a lengthwise document has more non-image areas to be read, thereby causing an increase in the amount of data to be read and the corresponding increase in the storage capacity.
Therefore, in this arrangement, a judgment is made as to whether image data in question is lengthwise or oblong, and if it is lengthwise, the image data is rotated by 90 degrees to convert it into data of an oblong image. Then, the data is compressed, and recorded; thus, it becomes possible to reduce the necessary storage capacity.
Moreover, Japanese Laid-Open Patent Publication No. 100769/1990 (Tokukaihei 2-100769) discloses an image display of the parallel processing system having the following modification. That is, in accordance with the data size of compressed image data, the amount of unit data related to the read-out process is controlled to have an optimum size; thus, this arrangement enables the parallel processing to exert its high-speed performance to the fullest extent in dealing with images having various data sizes, thereby shortening the time required for displaying.
The following is a detailed description of this arrangement. The image data is stored in a compressed manner. Compressed image data, read out from the storage apparatus, is temporarily stored in an compressed-image-data buffer. The compressed image data is decompressed and restored so as to return it to original image data before having been subjected to the compression. The original image data, thus restored, or display-use image data obtained by enlarging or reducing the original image data, is temporarily stored in an image buffer. The display-use image data is read from the image buffer, transferred to a frame memory, and displayed on a display section.
In this case, the read-out process of the compressed image data and the restoration, enlargement and reduction processes of the compressed image data are carried out in a parallel manner. Here, since the data size of compressed image data corresponding to one sheet varies indiscriminately, the time-shortening effect of the parallel processing cannot be fully exerted if the data size and the amount of unit data related to the read-out process do not match each other. For this reason, the data size of compressed image data in question is preliminarily retrieved, and a buffer size suitable for the data size found by the retrieval is maintained. In other words, the amount of unit data of compressed image data, which is read during the read-out process for one time, is varied. As a result, the time-shortening-effect of the parallel processing is exerted to the fullest extent, and it becomes possible to shorten the time required for displaying images having various data sizes.
However, the problem of this arrangement is that, when the remaining storage capacity of the storage medium becomes small or an overflow occurs in the data storage due to inputs of new image data to the storage medium, the user has to judge the relative degree of importance with respect to image data that has already been stored in the storage medium, and compress or erase date successively starting with the data having the lowest degree of importance. This imposes troublesome jobs on the user. Moreover, the data-compressing techniques disclosed in the above-mentioned Patent Publications merely show one method for data compression, and therefore fail to solve the above-mentioned problems.
Furthermore, in a network printer system wherein a plurality of host machines and printers are connected, there is a relatively long distance in most cases between the host machine on which the user is working and the printer in question. Therefore, it is quite natural that, while the user is going to get the printed matter, other people might see and read the printed matter, and if the printed information is a classified document which should not be disclosed to others, a serious problem might occur.
In recent years, there has been an increased demand for security protection to avoid such problems, and the following system has been commonly used in facsimiles and other apparatuses: data of confidential prints is accumulated in a storage device, and an ID code, entered in the printer, and an ID code, entered upon receipt of the printed data, are compared with each other, and the corresponding print-out operation is carried out only when both of the codes match each other.
Japanese Laid-Open Patent Publication No. 143253/1993 (Tokukaihei 5-143253) discloses a network printer system that is arranged as follows:
In the case when a printer does not have a storage device with a large capacity, an ID code is entered to the printer, while a host machine is kept at a stand-by state for confidential print. The printer transmits the ID code, thus entered, to the host machine. Upon receipt of the ID code, the host machine transmits the data of confidential prints corresponding to the ID code, and the printer outputs the received print data.
In the case when a printer has a storage device with a large capacity, the host machine transmits the data of confidential prints to the printer together with the ID code, and the printer stores the ID code and the data of confidential prints in its storage device. An ID code is entered to the printer, and only when the ID code, thus entered, and the stored ID code match each other, the data of confidential prints is read out, and printed out.
If a judgment is made that there is not a sufficient space capacity in the storage while the data of confidential prints are being transmitted from the host machine to the printer, the receipt is terminated, and the stored print data is erased. Further, the fact that the confidential prints have not been completed is stored, and the fact of the incompletion can be confirmed later by an output of the corresponding list.
The concept of confidential prints, itself, is a well-known technique as is disclosed in the above-mentioned Japanese Laid-Open Patent Publication No. 143253/1993 (Tokukaihei 5-143253). In the confidential print functions of printers for which a strong demand has been raised, the current subject is to provide techniques for achieving more effective use of confidential prints. Specific problems with the prior art are shown as follows:
In accordance with the prior art (Japanese Laid-Open Patent Publication No. 143253/1993 (Tokukaihei 5-143253)), if there is not a sufficient space capacity in the storage installed in the printer (that is, if it is not possible to store the transmitted confidential print data), the transmitted confidential print data has to be discarded, and this information is transmitted to the host machine, which is the original transmitter, or is stored so that it can be confirmed later on by the corresponding print out. Thus, the user who has transmitted the data is requested to re-transmit the confidential print data in question. This arrangement is due to the fact that since storage devices are very expensive, storage devices to be installed in the printer should be kept in a minimum.
Moreover, in accordance with the prior art, if there is not a sufficient space capacity in the storage device in the printer because of confidential print data that have been stored therein beforehand, data of confidential prints, next transmitted, have to be discarded, and in this case, the problem is that the user has to wait until the preceding data of confidential prints have been outputted to form a sufficient space capacity in the storage device, before he re-transmits the data.
Furthermore, in accordance with the prior art, the compression of confidential print data stored in the storage device is carried out irrespective of the time when the user tries to get data of confidential prints printed out, based on other conditions, for example, based on the order of preference which the user has manually instructed according to his intention. The resulting problem of this arrangement is that even if data of confidential prints are transmitted from the host machine so as to get them printed out immediately, it takes a long time to restore the print data in the case when the print data in question have been compressed.
Moreover, in the prior art, in an arrangement where data of confidential prints are compressed in order to effectively use the capacity of the storage device installed in the printer, even if some of the data of confidential prints have been printed out therefrom to form a sufficient space capacity in the storage device, the rest of the data still remains in a compressed state. Therefore, the user has to restore data of confidential prints before they are printed, and the resulting problem is that an increased working time is required due to the restoring process.
Furthermore, another problem with the prior art is that in the case when new data of confidential prints are received immediately after some compressed data of confidential prints have been restored, the efficiency of the system tends to deteriorate since either of the data of confidential prints has to be compressed again.